1. Field of the Invention
The invention relates to methods, and related apparatus, for controlling processing entities used, for instance, in communication systems such as for the control of signalling traffic between a signalling gateway and a plurality of application server processes.
2. Background Art
Establishing connections between two telephones involves a complex interaction of digital messages, hereinafter referred to generally as signalling. Nowadays telephone systems perform what is known as “out-of-band” signalling. Out-of-band signalling means that the communications required between the switches and other equipment in the network take place on communication channels other than the channel by which the voice or data flows. Typically, the out-of-band signalling takes place by means of digital communication channels. Thus, the public switch telephone network (PSTN) generally uses two types of channels, media and signalling.
Several protocols have been defined for out-of-band signalling. The most commonly used protocol, in North America, Asia and Europe, is known as Signalling System No. 7 (SS7). However, the SS7 protocol defines more than just a protocol for communication between switches. It also defines an entire switching network for facilitating signalling for call establishment, routing, and information exchange functions of switched circuit networks.
Since the amount of data transferred over data networks is now much larger than the voice traffic that is carried over the PSTN, carriers are in the process of consolidating both types of networks. In addition, telecommunication networks are increasingly making use of standard computing hardware in order to reduce IT costs.
Therefore, there is a trend in the telephone industry to migrate telephone systems using SS7-based networks for signalling to Internet Protocol (IP) networks. The Internet protocols are standardised by the Internet Engineering Task Force (IETF). Moving either or both of the media and signalling channels to an IP infrastructure involves the use of very different technologies and can be done independently. One IETF working group, called the Sigtran Group, is defining the protocols for back-hauling SS7 signalling messages across IP networks. Generally speaking, signalling across an IP network involves replacing the lower levels of the SS7 layered protocol communications and transport layers with IP network protocol communications and transport layers.
The IETF in collaboration with the Sigtran group have taken the initiative to define open standards for transporting SS7 over IP networks. With Sigtran technology, telephone services which today lie on top of SS7 networks, can run Application Servers (ASs) lying on top of IP networks. The interworking with SS7 networks is performed by Sigtran signalling gateways (SGs).
To enhance the availability of the signalling gateway, it can be distributed over several processes running in one or several computers, each of them being a Signalling Gateway Process (SGP). Every SGP belonging to a particular SG has the same SS7 point code (or the same list of PCs), with each SGP being connected to the SS7 network through redundant links.
On the IP side, each SGP is connected to Application Servers running the services. Each Application Server, which can typically be identified with a single logical service, such as a Short Message Service Centre (SMSC), can be implemented in a distributed manner by one or more processes or computers—referred to as the Application Server Processes (ASPs). To provide improved reliability, each SGP is typically directly connected to each ASP through an SCTP association such that there is one association between each SGP and each ASP.
A function performed by the signalling gateway is to receive SS7 signalling messages and direct them to the appropriate AS. To do so, the SG identifies a routing key (RK) defined by the M3UA or SUA protocol, which uniquely identifies the AS in accordance with parameters in the SS7 message. In general, the RK parameters are found in the header of the SS7 message. However, it may be desirable to take into account other elements of the message, such as a SMS originating number or some other aspect of the message content, in order to direct the message to the appropriate AS.
However, this variety of possibilities for the routing key definition can lead to problems in that in some circumstances the signalling information field of a single TCAP message may be too small to carry all the elements that might define a routing key.
This invention is directed to enabling a signalling gateway to act as a conduit for a transaction in which routing key information are not transmitted to the gateway at the beginning of a transaction message exchange and without requiring either the signalling gateway or any application server to have to manage a context for the transaction.